The present invention relates to a method for the preparation of a purified aqueous hydrogen peroxide solution or, more particularly, to a method for the preparation of an aqueous hydrogen peroxide solution highly purified relative to metallic and inorganic impurities and suitable for use in the manufacturing process of semiconductor devices.
As is known, aqueous hydrogen peroxide solutions are currently produced by the method of autoxidation while one of the serious problems in the products produced by this method is that the aqueous hydrogen peroxide solution is contaminated with various metallic or inorganic impurities such as aluminum and the like originating in the materials constituting the structure of the production plant. For example, commercial products of hydrogen peroxide solutions, of which the concentration of hydrogen peroxide is 10 to 70% by weight, usually contain such metallic and inorganic impurities in an amount of as large as several hundreds of .mu.g per liter. While aqueous hydrogen peroxide solutions are demanded in large quantities in the semiconductor industries, on the other hand, the hydrogen peroxide solutions used in these fields are required to have an extremely high purity containing metallic and inorganic impurities in an amount of as small as a few .mu.g per liter or even smaller as a standard product. Accordingly, it is indispensable that the hydrogen peroxide solution obtained by the autoxidation method is subjected to a purification to remove the metallic and inorganic impurities as completely as possible when the intended use of the product is in the semiconductor industries.
Various methods have been proposed heretofore for the purification of an aqueous hydrogen peroxide solution relative to the metallic and inorganic impurities including a method in which an aqueous hydrogen peroxide solution containing metallic and inorganic impurities is passed through a bed of a cation-exchange resin so as to remove the cationic impurities by the ion-exchange reaction on the resin. This method, however, has problems that, although strongly cationic impurities of metals can be removed by merely bringing the solution into contact with the cation-exchange resin, the method is not effective for the metallic impurities not completely soluble or only weakly ionic impurities in an aqueous hydrogen peroxide solution such as, in particular, aluminum and anionic impurities originating from the metal-containing compounds which can assume both cationic and anionic forms in themselves such as aluminum, iron, chromium and the like. While sulfate anions are released in large quantities from the cation-exchange resin by the degradation of the sulfonate groups on the resin, the method is ineffective for the removal of the sulfate anions.
It is of course known that anion-exchange resins are effective for the removal of inorganic impurities from an aqueous hydrogen peroxide solution by passing the solution through a bed of the anion-exchange resin. It is known that contacting of an aqueous hydrogen peroxide solution, after a treatment in advance with a cation-exchange resin, and a strongly basic anion-exchange resin in the hydroxy-form is effective for the removal of inorganic impurities which can be removed by a mere contact with a strongly acidic cation-exchange resin.
However, purification of an aqueous hydrogen peroxide solution by use of a strongly basic anion-exchange resin in the hydroxy-form has some problems that, for example, decomposition of hydrogen peroxide is accelerated when the solution is brought into contact with the strongly basic anion-exchange resin. Decomposition of hydrogen peroxide is further accelerated when the aqueous hydrogen peroxide solution contains metallic impurities of iron, chromium and the like.
Furthermore, the method of contacting of an aqueous hydrogen peroxide solution with a strongly basic anion-exchange resin in the hydroxy-form is not effective for the removal of the metallic impurities not completely soluble in the solution and weakly cationic and anionic metallic impurities so that highly purified hydrogen peroxide solutions suitable for use in the manufacturing processes of semiconductor devices can hardly be obtained by these conventional methods.
Japanese Patent Publication 35-16677 teaches that anion-exchange resins can be used for the purification of aqueous hydrogen peroxide solutions when the anion-exchange resin is converted from the hydroxy-form into the hydrogencarbonate-form or carbonate-form so as to decrease the basicity of the resin. Further, Japanese Patent Kokai 5-17105 teaches that the decomposition of hydrogen peroxide can be prevented by the addition of an acid to the hydrogen peroxide solution in the contacting treatment of the solution with an anion-exchange resin.
These methods, however, are not quite satisfactory to comply with the requirement for the complete removal of metallic impurities not completely soluble in the aqueous hydrogen peroxide solution or weakly cationic and anionic metallic impurities so that a highly purified hydrogen peroxide solution as desired cannot be obtained by these methods. Furthermore, these methods are not practically applicable to the purification of an aqueous hydrogen peroxide solution due to the difficulty in completely preventing decomposition of hydrogen peroxide caused by the remaining metallic impurities.